Lighting fixtures can be automatically switched on at dusk and off at dawn using twist-lock photoelectric controllers. The lighting fixtures may be used to light roads, parking lots and other areas outdoors. The photoelectric controller senses the intensity of the ambient light and switches the lighting fixtures on and off as appropriate. The photoelectric controllers are typically oriented so that the photosensor faces North, away from direct sunlight in the Northern hemisphere (and in a southerly direction in the Southern hemisphere). It is also desired to be able to easily adjust the receptacle that receives the photoelectric controller to achieve the desired orientation.
Lighting fixtures for street lights typically include an electrical receptacle that receives the photoelectric controller that is mounted to a housing on the top of the lighting fixture. The electrical receptacle is wired to the power supply of the lighting fixture. The photoelectric controller has three main terminals that are inserted into the electrical receptacle and twisted to lock the photoelectric controller to the receptacle.
In particular, the widely adopted standard for outdoor lighting fixtures includes a NEMA standard 3-terminal polarized twist-lock receptacle mounted to the top of the cobra head fixture, with the photoelectric (PE) detector housed in a module that plugs into the twist-lock receptacle and which allows rotation of the PE module so that the photo sensor faces generally North. The PE module includes a three-terminal twist-lock type connector coupleable to the twist-lock receptacle to provide three class 1 electrical connections between the controller module and the fixture assembly. In operation, the fixture is wired with the AC line connection wired from the fixture conduit to one terminal of the twist-lock receptacle and the input neutral wired to a second terminal of the twist-lock receptacle. The third twist-lock receptacle wire is connected to the light source ballast or driver and the PE module provides a switch connection between the AC line wire and the third twist-lock receptacle wire for selective connection/disconnection of power to/from the ballast or driver. This configuration allows easy replacement of the PE module, and such apparatus has served outdoor public areas as well as industrial, commercial, and residential lighting needs for many years. However, improved energy utilization is desirable by which outdoor lighting fixtures can be intelligently used to provide lighting without consuming excessive energy.
The orientation of the photoelectric controller in the Northern direction is accomplished by the use of a metal snap ring having fingers that engage the electrical receptacle and urge it toward the housing of the lighting fixture using a spring force. This is disclosed in U.S. Pat. No. 4,477,143. The electrical receptacle may be lifted up against the spring force and turned to orient the receptacle North. Circumferential holes located in an upper circular end plate of the electrical receptacle receive pins formed around an opening in the housing for securing the electrical receptacle to the housing. In another approach in which no snap ring is used, the electrical receptacle is oriented by loosening a screw in the top of the receptacle, rotating the receptacle until indicia on the receptacle points to the desired position and then re-tightening the screw.
The photoelectric controller is subjected to harsh environments at certain times and at certain locations. For example, the photoelectric controller may be used to control streetlights in arid climates where there are dust storms. It also may be subjected to snow and ice. The window may become coated with dust, snow and ice, interfering with proper operation of the photosensor. Maintenance vehicles will periodically spray the photoelectric controller with high pressure water to clean the window. High pressure water spray, high velocity dust, snow, ice and extended periods of direct sunlight is a problematic environment for a high voltage electronic device to be subjected to.